1. Field of the Description
The present description relates, in general, to robots such as robotic characters for use in the entertainment industry and such as robots for interacting safely with humans in other applications. More particularly, the present description relates to techniques for actuating joints, such as rotational joints, in robots in an effective (e.g., responsive and rapid movements) and safe manner.
2. Relevant Background
With the development of new engineering techniques, miniaturization of electronics, and the increase of computing power, designers are now able to design robots or robotic devices that can perform many intricate tasks including cooperative or interactive tasks with humans. While many have predicted a much more rapid expansion of the use of robots in industry, at home, and in entertainment applications, safety implications have created barriers that designers must address and overcome as most robots have the potential to cause damage to their surroundings including humans that may be nearby.
As one example, a biped humanoid robot is a robot with an appearance based on that of the human body. Humanoid robots have been designed for providing interaction with various environments such as tools and machines that were made for humans and often are adapted for safely and effectively interacting with human beings. In general, humanoid robots have a torso with a head, two arms, and two legs each with some form of foot such that the robot can walk on planar surfaces, climb steps, and so on. Humanoid robots may be formed with many rigid links or skeletal components that are interconnected by joints (such as rotational joints) that are operated or positioned through electronic controls of drive motors that apply a force or torque to each joint to move and position a robot.
In order to interact with human environments, humanoid robots require safe and compliant control of the force-controlled joints. In this regard, a controller is provided for each robot that has to be programmed to determine desired motions and output forces (contact forces) and, in response, to output joint torques to effectively control movement and positioning of the humanoid robot. However, it has often proven difficult to achieve desired results with force-controlled robots because while performing a task in a complex environment the robot may encounter uneven ground or even steps, static and dynamic obstacles, and even humans.
A number of useful techniques have been developed for controlling humanoid robots, but, regardless of the specific control techniques implemented by the robot controller, particular data that may be provided by sensors or be calculated has to be accurate for adequate control to be achieved. As one particular example with regard to kinematic parameters, a robot may include a sensor at each joint that is used to provide input to the controller for identifying or determining joint angles, and these joint angles are kinematic parameters used to further control and/or position the robot through movement of its joints.
These and other examples of robots and robotic applications shows show that robots are often designed to perform specific tasks involving speed and precision. Typically, these robots utilize high performance and/or powerful hydraulic or electric motors to actuate or move the skeletal limbs or rigid links by, for example, moving a joint between two of these limbs or links. In order to make these robots safe around humans, their speed and power are mitigated by the use of sensors and complex control hardware and software. Neither the hydraulic actuator nor the electric motor-based actuator is inherently compliant such that robots with these actuators must rely, therefore, on the control system to make them safe (e.g., compliant when in contact with their surroundings if needed such as when in contact with a human). As a result of these and other design requirements, many of these robots are complex and expensive to design, build, and maintain.
In many settings, robots may have differing design criteria that would not require as precise of movement or may require less force to achieve desired functions. For example, robotic characters in theme park attractions or in many human-interactive settings are not required to perform tasks that include high-precision movements. Instead, these robots or robotic characters simply may need to be expressive or to move in a “life-like” and repeatable manner. In other words, these robots may just need to act such as to wave their hand, move their fingers, turn their heads, and so on, but these actions need to be done in a manner that is deemed safe around humans. Presently, these characters have been implemented using hydraulic or electric actuators that, as discussed above, require complex control systems to operate safely.
Hence, there remains a need for improved methods and devices for allowing a robot to be moved or actuated in a less complex manner but while still meeting or exceeding all safety demands for use with or nearby humans.